The present invention relates to dynamoelectric machines and particularly to acyclic (homopolar) generators utilizing liquid metal current collectors.
In acyclic (homopolar) generators the interaction of the component of the magnetic field normal to the plane of the current collectors, i.e., aligned with the path of current between stator and rotor, and the rotor peripheral velocity establishes a voltage which develops circulating currents in both solid brush and liquid metal current collectors. These circulating currents produce additional electrical losses in the generator under load conditions by creating a non-uniform current distribution at the collector. Circulating currents also increase open circuit or no load losses by virtue of the resistive losses in the collector tip and brushgear. Such open circuit losses are proportinal to the square of both the flux density of the normal magnetic field component and the collector tip velocity. In the case of liquid metal collectors, the additional resistive losses imposed by circulating currents raise the temperature of the liquid metal, and thus its flow rate must be increased to limit this temperature rise to acceptable levels. Excessive liquid metal temperatures raises its electrical resistivity and alters its mass density from that to which the structure for containing the liquid metal in the collector region against electromagnetic expulsion forces is designed.
A goal of present research and development efforts is to develop smaller, ultra-high current acyclic genrators of dramatically increased power density. Increases in the magnetic flux density and/or peripheral velocity of the acyclic machinery are required to develop the necessary generator voltages. Liquid cooled copper armatures and compensating conductors are required to carry the ultra-high currents. This results in larger air gaps between the stator and rotor. The combination of increased flux densities and air gap length increases the magnitude of the fringing or leakage fields in the liquid metal collector region. All of these factors contribute to high power densities, as well as to increased circulating currents and associated electrical losses in the liquid metal collector region of acyclic generators.
It is accordingly an object of the present invention to provide an acyclic generator having an improved liquid metal current collector.
A further object is to provide an acyclic generator wherein the magnetic field in the region of the liquid metal current collectors is shaped to reduce the magnitudes of circulating currents.
A further object of the present invention is to provide an acyclic generator of the above-character wherein the components of the excitation magnetic field in the liquid metal current collector region are reduced.
Another object is to provide an acyclic generator of the above-character wherein the magnetic field component normal to the plane of the liquid metal collector is minimized.
Other objects of the invention will in part be obvious and in part appear hereinafter.